This application is designed to train Dr. John Halpern to be an independent investigator with special skills in assessing both neuropsychological effects and cultural aspects of substance abuse. Dr. Halpern is now completing a third-year postdoctoral fellowship in substance abuse research at the Alcohol and Drug Abuse Research Center, McLean Hospital, Harvard Medical School-a nationally recognized major substance abuse research facility. Dr. Halpern has already published several peer-reviewed papers on substance abuse, most recently a critical review of studies of the long-term neuropsychological effects of hallucinogens-a class of drugs increasing in popularity among high school students and young adults, 1,2 yet still inadequately studied. Dr. Harrison G. Pope, Jr., the proposed mentor for this project, is a well-recognized substance abuse investigator with an established record of mentoring junior investigators. With Dr. Pope's guidance, Dr. Halpern has already obtained pilot data assessing neuropsychological performance in 42 Native Americans. Ten of these subjects are members of the Native American Church. The practitioners of this religion are virtually unique in North America in that they extensively ingest a hallucinogen, the peyote cactus, but typically use no other drugs. Thus, they offer a valuable opportunity to assess the long-term effects of hallucinogen use without the confounding effects of other substances. Dr. Halpern has also obtained pilot data on comparison groups of 11 Native Americans with past alcohol dependence and 21 Native American controls. Under Dr. Pope's mentorship, Dr. Halpern proposes to expand this work over the next four years to study an additional 210 Navajo subjects: 70 peyote users, 70 former alcohol users, and 70 controls. These data will provide information of major public health significance, both for the Native American population itself and for the population at large, regarding the long-term neuropsychological effects of hallucinogens and alcohol. Dr. Halpern will supplement this work with a full program of courses in the Harvard School of Public Health, leading to an MPH degree within the four years, and with continued didactic experience with Dr. Pope and other investigators at the Alcohol and Drug Abuse Research Center. This program will enable Dr. Halpern to become an experienced investigator, capable of designing and performing future studies independently.